(1) Field of the Invention
The present invention relates to the field of variable focal lenses, and more specifically to liquid lenses having a variable electrically controlled focus.
(2) Description of Related Art
An article of B. Berge entitled “Electrocapillarité et mouillage de films isolants per l'eau” published in 1993 in C.R. Acad. Sci. Paris, t. 317, serial II, pages 157 to 163, discloses a device comprising a drop of conductor liquid placed on a dielectric film covering a flat electrode. A voltage may be applied between the liquid conductor drop and the electrode. This article describes a theoretical study of the wetting variation of a dielectric material with respect to a conductor liquid and shows that the wetting increases substantially in presence of an electric field caused by the voltage existing between the conductor liquid and the electrode. This phenomenon is called electrowetting by the author.
U.S. Pat. No. 5,659,330 discloses a display device using the electrowetting phenomenon to vary the shape of a drop of opaque conductor liquid placed on a dielectric. This document does not suggest the use as an optic lens.
An article of Vallet, Berge and Vovelle, “Electrowetting of water and aqueous solutions on poly(ethylene terephthalate) insulating films”, published in Polymer, Vol. 37, No 12, pages 2465 to 2470, 1996, discloses a deformation of a liquid conductor drop to which a voltage is applied. It is indicated that, when the applied voltage becomes too high, the surface of the drop becomes unstable, and microdroplets may be ejected at the periphery of the drop.